The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Efforts have been made in the past to match the impedance of an incoming signal to an output load. For example, U.S. Pat. No. 8,254,601 to Feldstein, issued Aug. 28, 2012, entitled “Impedance Matching Speaker Wire System” teaches a compensation circuit connected in series with a speaker system and an incoming signal. More specifically, Feldstein describes a coaxial line having a predetermined characteristic impedance wherein the circuit is configured with circuit components that allow for adjustment of the impedance of the output circuit. Moreover, in Feldstein, the range of frequencies the tuning circuit can process is limited due to its predetermined characteristic impedance resulting in inefficient filtering of some frequencies. As a consequence of the solution presented in Feldstein, the fidelity and level of definition in the music is significantly impaired.
Additional efforts have been made through the use of capacitors. U.S. Patent Publ. 2007/0189554 to Innis, published Aug. 16, 2007, entitled “Audio speaker including impedance matching circuit” teaches impedance matching through integrated circuitry. By configuring the capacitors in parallel, a user can engage a switch to selectively shunt electrical current around the capacitors. The result is altering of effective speaker impedance. By quantifying the value of the speakers, the matching circuit in Innis is limited to only matching certain predefined input values. Consequently, the efficiency of the matching circuit is generally not optimal.
Other efforts have been made to achieve reflectionless impedance matching. U.S. Pat. No. 1,832,452 to Feldtkeller et al. teaches a telephone interconnecting circuit that, by proportioning resistances to a transmission line, allows for termination that is practically free from reflection and attenuation from a transmitter to loud speakers. This solution, however, fails to take into account that audio signals—unlike transmission line signals—can contain many different frequencies, and thus using a resistor (a static component) to match impedance is suboptimal over a range of frequencies.
U.S. Pat. No. 7,747,228 to Kasha et al. similarly shows efforts made to reduce signal reflection via impedance matching. Kasha et al. teaches the use of an impedance matching component placed between an amplifier output and an antenna. The result is that signal reflections are either reduced or eliminated. This reference, however, does not provide any detail as to what type of component might be used to achieve the goal of reflectionless impedance matching.
U.S. Patent Application No. 2009/0175378 to Bogdan et al. teaches a system capable of matching impedances over a wide range of radio frequencies or other high frequency ranges. To accomplish this, it digitally transforms a first load impedance into a second load impedance. However, this reference fails to teach impedance matching using passive components.
U.S. Application No. 2013/0325149 to Manssen et al. teaches a circuit that can tune impedance to match a frequency coming into an antenna. However, this reference requires active controlling to create matched impedance and thus fails to appreciate that impedance matching can be achieved using passive components.
U.S. Pat. No. 8,190,109 to Ali et al. describes a system of active impedance matching. It measures the amount of reflected energy and then, using that value, varies the impedance of a component in the system before making another measurement and making another adjustment. In other words, Ali et al. teaches a closed-loop control system for impedance matching. In this way, it can converge on a solution resulting in substantially reflectionless matching. This system, as with Manssen et al., fails to appreciate that substantially reflectionless impedance matching can be achieved without the use of a feedback loop.
U.S. Pat. No. 8,472,907 to Yamagajo et al. teaches an antenna system that includes one or more impedance matching elements. However, devices of this reference fail to teach impedance matching over a range of frequencies.
Other related references are similarly deficient. See U.S. Patent Application No. 2010/0081379, U.S. Patent Application No. 2011/0159832A1, U.S. Pat. No. 4,006,315, U.S. Patent Application No. 2007/0201707.
Thus, there is still a need to further improve the power efficiency of a speaker circuit by providing substantially reflectionless impedance matching using passive circuit components that allow for impedance matching over a wide range of frequencies.